The invention provides an emergency control method based on a cascading failure damage degree index and belongs to the technical field of electric power systems and automation thereof. The method, according to an operation state of an electric power system in occurrence of cascading failures, evaluates damage to the system caused by the cascading failures; the method takes the influences of the failures on three aspects of the operation states of other components, a network topological structure and load loss into account, predicts following failures according to power flow redistribution conditions resulting from an initial failure, and estimates the damage degree thereof on the basis. Thus, auxiliary judgment of the developing process of cascading failures is performed according to the numerical value of the damage degree and the growth trend of the numerical value, and then it is judged whether emergency control measures should be taken timely after the occurrence of failures, and corresponding measures are taken to obstruct the cascading failures.